Purification of vinyl acetate by distillation and scrubbing of the distillate



No 1947- v. L. HANSLEY ET AL 2,431, 54 PURIFICATION OF VINYL ACETATE BYDISTILLATION AND SCRUBBING OF THE DISTILLATE Filed 001:. 25, 1944 2CONDENSER AND SCRUBBER FRAc'nouA'r'ms COLUMN VivyilL.HansleypquLlhMayill INVENTORS ATTORNEY Patented Nov. 25, 1947 UNITED STATESPATENT OFFICE.

PURIFICATION OF VINYL ACETATE BY DIS- TILLATION AND SCRUBBING OF THEDIS- TILLATE Application October 25, 1944, Serial No. 560,300

3 Claims. (01. 202-67) moval of impurities from volatile organicliquids.-

More particularly, it relates to a combined process of distillation andextraction for the removal of such impurities from volatile organicliquids.

In conventional distillation methods for the separation of impuritiesfrom volatile organic liquids, it is frequently necessary to carryoutthe distillation by a series of elaborate and expensivestills'requiring the redistillation of a considerable proportion of theliquid being purified. Such redistillation of intermediate cuts ofliquids necessarily involves losses by volatilization and handling. Ifthe liquid to be purified is polymerizable, losses due to unavoidablepolymerization are also entailed.

It is an object of this invention to provide a new and improved processfor the removal of impurities from vinyl acetate. It is another objectof this invention to provide a process for removal of impurities fromvinyl acetate which very considerably simplifies the removal of tracesof impurities that are difficult to separate from the liquids bystraight-forward distillation.

It is a further object of this invention to provide a process for theremoval of impurities from easily polymerizable volatile organic liquidssuch as vinyl acetate which will reduce the tendency of the liquid topolymerize. I

It is yet another object of this invention to provide a distillationprocess for the removal of impurities from vinyl acetate which processinvolves an improvement in distillation efiiciency, and a reduction inthe rehandling of the liquid whereby losses by evaporation, and in somecases by polymerization, are greatly reduced.

It is still another object of this invention to provide an improveddistillation process for the removal of traces of diflicultly removableimpurities from vinyl acetate, which process will reduce the period ofthe distillation and will reduce the tendency of the vinyl acetate topolymerize.

Other objects of the invention will appear hereinafter.

In accordance with the present invention, the above objects areaccomplished by a combined distillation and liquid extraction processcomprising subjecting the volatile, organic liquid containing impuritiesto distillation in a fractionating column, passing the vapors from thetop of the fractionating column into direct contact with a scrubbingliquid whereby to condense and scrub the same simultaneously. Thecondensing and scrubbing liquid is substantially immiscible with theliquid (condensed vapors) but which will retain a proportion of theimpurities, at a temperature below the boiling point of the distilledliquid, separating the distilled liquid from the scrubbing liquid, andreturning the purified distilled liquid to the top of the fractionatingcolumn until the desired amount of impurities have been removed from theliquid being distilled, after which the purified liquid is collected.

The process of the present invention may be carried out by means of anysuitable apparatus; The accompanying illustration shows one embodimentof apparatus suitable for this purpose. The following detaileddescription, when taken in connection with the accompanying drawing isbelieved to clearly disclose the principles of the invention to enableanyone skilled in the art to practice the same.

In the drawing the figure is a diagrammatic elevational view of a stilland fractionating column combined with an extraction apparatus.

Referring to the figure of the drawing, reference numeral I designates astill pot and fractionating column into which the volatile organicliquid to be purified is placed and heated to vaporize the same. Thevapors-from the head of the fractionating column are passed to acondenser 2 into which a scrubbing liquid is slowly admitted at atemperature to condense the vapors. The scrubbing liquid may be'composedof any liquidwhich is substantially immiscible with the condensed liquidand which will retain a substantial proportion of the impurity to beremoved from the condensed liquid. The combined condensate and scrubbingliquid is conducted to the gravity separator 3 where the two liquidswhich are substantially immiscible with each other are separated intotwo layers i and 5. In the apparatus illustrated in the drawing, thescrubbing liquid is the heavier liquid and is automatically removedthrough over-flow pipe 6. The lighter condensate is passed from thelayer 5 to the top of the irac-, tionating column through pipefil.Obviously, ii

' the distillate were heavier than the scrubbing liqdesired extent.

uid, the lower layer would be'passed to the top of the fractionatingcolumn and the upper layer would be removed by over-flow. Thedistillation and: scrubbing operation is continued until ,a samplewithdrawn at H indicates that the im-v purity has been removed from thedistillate to the The purified organic liquidiis then collected at H byclosing valve 9 and opening valve l0. During this final collectionperiod, the' scrubbing liquid may be continuously passed into thecondenser 2 with the purified vapor to 3, condense the latter, in whichcase the scrubbing liquid and purified condensate will have to beseparated in another container. On the other hand, the condenser 2 maybe provided with a cooling jacket, or cooling tubes, through whichcooling liquid is circulated during final collection of the condensate,in which case no scrubbing liquid is passed into condenser 2 during thecollection period.

The process, generally described above, has been found to be ofparticular utility in the purification of vinyl acetate containingdiflicultly removable impurities. This process has, for example, beenfound of great utility in the purification of vinyl acetate containingtherein, as impurities, acetic acid and acetaldehyde. Vinyl acetate isvery easily hydrolyzed to produce acetic acid and acetaldehyde and,therefore, it is very diflicult to substantially free it from thesehydrolysis products. l

The following detailed example is given to illustrate the preferredprocedures for the purification of vinyl acetate.

Example I Crude vinyl acetate, 1000 a., was charged into the distillingand extracting apparatus of Fig. 1. The composition of the crudecharging stock was:

Cc. Vinyl acetate 830 Acetaldehyde, acetone, water 90 Acetic acid 80Plain water at the rate of 150 lbs/hr. was introduced into the condenser2 in Fig. 1 with a 300 lb./hr. boil-up total reflux in still i until thehead temperature reached 71 C. This temperature corresponded to a 0.03%total acetaldehyde and acetone content in the condensate returning tothe still column. The scrubbing was accomplished on a continuous basis.The difference in specific gravity and immiscibility of the water ,andvinyl acetate gave an automatic overflow of each phase, the acetaldehydeand acetone going over 6 dissolved in water and the vinyl acetate phasereturning to the column I. The scrubbing was complete at the 71.0 C.head temperature and the following cuts were made at the 300 lb./hr.boil-up rate:

Cut (1) '71.0 C. to 71.8 C. at 1521 reflux Cut (2) '7l.8 C. to 73.0 C.at 221 reflux Cut (3) 73.0 C. to l10.0 C. at 1521 reflux impurity to beremoved.

Since it is obvious that many changes and modifications can be made inthe above-described details without departing from the nature and spiritof'the invention, it is to be understood that the invention is not to belimited to the said details except as set forth in the following claims.

We claim:

1. A process for the removal of impurities from vinyl acetate whichcomprises subjecting said acetate containing impurities to distillationin a fractionating column, passing the vapors from the top of saidcolumn into contact with a scrubbing liquid at; a temperature below theboiling point of the distilled liquid whereby to condense said vapors,said scrubbing liquid being immiscible with vinyl acetate but which willretain a proportion of saidimpurities, separating the vinyl acetate fromthe scrubbing liquid and returning the vinyl acetate to the top of saidfractionating column until the desired amount of impurity has beenremoved therefrom, and collecting the purified vinyl acetate.

2. A process for the removal of acetaldehyde and acetone from vinylacetate which comprises subjecting said acetate containing acetaldehydeand acetone to distillation in a fractionatlng column, passing thevapors from the top of said column into contact with a scrubbing liquidat a temperature below the boiling point of the distilled liquid wherebyto condense said vapors, said scrubbing liquid being immiscible withvinyl acetate but which will retain -a proportion of said aldehyde andacetone, separatingthe vinyl acetate from the scrubbing liquid andreturning the vinyl acetate to the top of the fractionating column untilthe desired amount of aldehyde and acetone has been'removed therefrom,and collecting the purified vinyl acetate.

3. A process for the removal of acetaldehyde and acetone from vinylacetate which comprises subjecting said acetate containing acetaldehydeand acetone to distillation in a fractionating column, passing thevapors from the top of said column into contact with an aqueous solutionof 45 sodium bisulfite at a temperature below the boiling point of thedistilled liquid whereby to condense said vapors and cause the condensedliquid to be scrubbed, separating the vinyl acetate from the scrubbingliquid and returning the vinyl ace- 50 tate-to the top of thefractionating column until the desired amount of acetaldehyde andacetone has been removed therefrom, and collecting the purified vinylacetate.

VIRGIL L. HANSLEY. PAUL L. MAGILL.

' REFERENCES CITED I The following references are of record in the fileof this patent:

UNITED STATES PATENTS Number Name Date 2,350,719 Bright et a1. June 6,1944 2,281,311 Knapp Apr. 28, 1942 5 1,918,283 Miller July 18, 19332,388,844 Hasche et a1 Nov. 13, 1945

